This application is based on Japanese Patent Application No. 2000-315186, filed in Japan on Oct. 16, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
This invention relates to a switching apparatus which employs the interaction of magnetic fields produced by opposing coils having currents flowing through them to generate a drive force which can contact or separate contacts to close or open an electric circuit.
2. Description of the Related Art
FIG. 5 is a schematic elevation of a switching apparatus known to the inventors for multiphase electric power (such as three-phase electric power) which utilizes electromagnetic repulsive forces to carry out switching to open and close an electric circuit. FIG. 5 shows the switching apparatus in a closed contact state. The switching apparatus of FIG. 5 includes a separate switching unit 20 for each phase of electric power with respect to which switching is to take place, and the plurality of switching units 20 (three units in this case) form one group. The switching units 20 are connected to a common power supply 30 by contact opening drive current supply lines 33, which conduct based on a contact opening command 31 from a contact opening command switch, and contact closing drive current supply lines 34, which conduct based on a contact closing command 32 from a contact closing command switch.
The three switching units 20 are supported by and secured to first through fourth support plates 15-18. The switching units 20 are separated from each other by electrically insulating posts 19 which prevent the occurrence of short circuits between phases.
Each switching unit 20 has a switch portion 3 having a fixed contact 1 and a movable contact 2 which is disposed opposite the fixed contact 1 and can move into and out of contact with the fixed contact 1. A movable shaft 4 extends from the movable contact 3, and an operating mechanism 5 is operatively connected to the movable shaft 4 to open and close the switch portion 3 by translating the movable shaft 4 in its axial direction.
The fixed contact 1 of each switch portion 3 is secured to the first support plate 15 through an electrical insulator. The fixed contact 1 and the movable contact 2 are housed in an evacuated bulb 6 in order to effectively extinguish an arc which is generated during contact opening or closing.
Each movable shaft 4 includes a live portion 8 connected to the movable contact 2 and a non-live portion 9 connected to the operating mechanism 5. The live portion 8 and the non-live portion 9 are connected to each other by an electrically insulating rod 7 which prevents current from flowing from the switch portion 3 to the operating mechanism 5. A movable electrically conducting connecting terminal 10 is installed on the live portion 8 to permit connection to an external conducting body (not shown).
The operating mechanism 5 includes an electromagnetic repulsion plate 11 secured to the non-live portion 9 of the movable shaft 4, a contact opening fixed coil 12 which is secured to the second support plate 16 and opposes the upper surface of the electromagnetic repulsion plate 11, a contact closing fixed coil 13 which is secured to the third support plate 17 and opposes the lower surface of the electromagnetic repulsion plate 11, and a nonlinear bidirectional biasing spring 14 which is secured to the fourth support plate 18 and the non-live portion 9 of the movable shaft 4 and which maintains an open contact state or a closed contact state of the switch portion 3. The non-live portion 9 of the movable shaft 4 loosely passes through the second support plate 16 and the third support plate 17, through the contact opening fixed coil 12 and the contact opening fixed coil 13 which are secured to these support plates, and through the fourth support plate 18 to which the biasing spring 14 is secured so as to be able to translate in its axial direction. As a result, the electromagnetic repulsion plate 11 can reciprocate between the contact opening fixed coil 12 and the contact closing fixed coil 13. The properties of the biasing spring 14 are such that when the point of connection between the movable shaft 4 and the biasing spring 14 moves past a neutral point of the biasing spring 14, the direction in which the biasing spring 14 exerts a biasing force is reversed.
Contact opening operation of the switching apparatus of FIG. 5 is performed in the following manner. When the apparatus is in the closed contact state shown in FIG. 5 in which the fixed contacts 1 and the movable contacts 2 of the switching portions 3 contact each other, if a contact opening command 31 is provided to the power supply 30 from the contact opening command switch, the power supply 30 causes a pulse current to be supplied to the contact opening fixed coil 12 of the operating mechanism 5 of each switching unit 20 through the contact opening drive current supply lines 33. This current causes each contact opening fixed coil 12 to generate a magnetic field, and the magnetic field causes an induced current to flow in the corresponding electromagnetic repulsion plate 11, which is in a position close to and opposite the contact opening fixed coil 12, so as to generate a magnetic field which is opposite in direction to the magnetic field generated by the contact opening fixed coil 12. Due to the interaction of the magnetic field which is generated by the induced current flowing in the electromagnetic repulsion plate 11 and the magnetic field generated by the contact opening fixed coil 12, each electromagnetic repulsion plate 11 receives an electromagnetic repulsive force urging it away from the corresponding contact opening fixed coil 12.
Due to this electromagnetic repulsive force, each electromagnetic repulsion plate 11 is moved downwards in the figure against the upwards spring force exerted by the biasing spring 14 in the contact closing direction. At the same time, the movable shaft 4 which is secured to the electromagnetic repulsion plate 11 and the movable contact 2 which is secured to the movable shaft 4 also move downward, and the fixed contact 1 and the movable contact 2 are made to separate from each other, whereby each switch portion 3 is opened. During this operating process, the biasing spring 14 which was exerting a biasing force in the contact closing direction inverts its direction of action and generates a biasing force in the contact opening direction when the movable shaft 4 moves downwards past the neutral point of the biasing spring 14. Accordingly, the open contact state of the fixed contact and the movable contact 2 is maintained by the biasing spring 14.
When the switching apparatus is in the open contact state, if a contact closing command 32 is input from the contact closing command switch to the power supply 30, the power supply 30 supplies a pulse current to the contact closing fixed coil 13 of each switching unit 20 through the contact closing drive current supply lines 34. Due to this current, the contact closing fixed coil 13 generates a magnetic field, which generates an induced current in the electromagnetic repulsion plate 11 which is close to and opposing it. As a result, the electromagnetic repulsion plate 11 generates a magnetic field which is in the opposite direction of that generated by the contact closing fixed coil 13. Due to the interaction of the magnetic field generated by the contact closing fixed coil 13 and the induced magnetic field generated by the electromagnetic repulsion plate 11, a repulsive force acts on the electromagnetic repulsion plate 11 urging it away from the contact closing fixed coil 13, and the electromagnetic repulsion plate 11 moves upward against the force of the biasing spring 14 acting in the contact opening direction. As a result of this upward movement by the electromagnetic repulsion plate 11 and the movable shaft 4 connected to it, the biasing spring 14 changes from exerting a biasing force in the contact opening direction to exerting one in the contact closing direction, and when the closed contact state of FIG. 5 is reached, the biasing spring 14 maintains this state.
In the switching apparatus of FIG. 5, the magnetic field which is generated by the electromagnetic repulsion plates 11 due to induction is small compared to the magnetic field which is generated by directly supplying current to a coil, so the electromagnetic repulsive force due to the interaction of the magnetic field generated by the fixed coils 12 and 13 and the magnetic field generated in the electromagnetic repulsion plates 11 due to induction is not efficiently generated. If it is attempted to increase the generated magnetic field by increasing the number of coil windings or by increasing the size of the power supply in order to increase the pulse current applied to the fixed coils, there is the problem that the apparatus as a whole becomes large. Furthermore, the apparatus of FIG. 5 performs the contact opening and closing operation with respect to a plurality of phases simultaneously, so there are cases in which an excessive current and voltage can be generated with respect to one of the phases, and equipment connected to the switching apparatus (such as a transformer or a motor) can be adversely affected.
An object of the present invention is to obtain a switching apparatus which can decrease the energy needed for switching, which can reliably perform switching at high speed, and which can prevent the occurrence of excessive currents or voltages during contact opening or closing operation.
According to one form of the present invention, a switching apparatus includes a plurality of switching units. Each switching unit includes a switch portion having a fixed contact and a movable contact which is movable with respect to the fixed contact between an open and a closed position to open and close the switch portion, a movable shaft which extends from the movable contact, and an operating mechanism having a fixed coil and a movable coil opposing the fixed coil and operatively connected to the movable shaft for translating the movable shaft in its axial direction. The switching apparatus further includes a power supply which supplies power to at least one of the switching units.
In preferred embodiments, each operating mechanism has two fixed coils disposed on opposite sides of the movable coil.
The plurality of operating mechanisms may be driven by a single power supply, or they may be individually driven by separate power supplies.
When the switching apparatus includes a plurality of power supplies, the power supplies may be independently driven by individual command signals.
The switching apparatus may also include current and voltage measuring devices for installation on each electric power line to which the plurality of switching units are to be connected for measuring current and voltage, and a phase sensor which senses the phase in each power line based on the current and voltage measured by the corresponding current and voltage measuring device. A switching controller can than determine the optimal timing for contact opening or contact closing of the switching units based on the current and voltage measured by the measuring devices and the phase determined by the phase sensor. The switching controller then outputs an optimal timing signal to each power supply, and the operating mechanisms are driven with the optimal timing.
The switching controller may be responsive to a contact opening or closing command to output a signal indicating the optimal timing for switching to each power supply based on the command, and the operating mechanisms can be driven with the optimal timing.
The switching apparatus may include a defect sensor which senses the occurrence of a defect based on the current and voltage measured by the current and voltage measuring devices and the phase sensed by the phase sensor. When a defect is sensed, the switching controller outputs a signal with the optimal timing to each power supply.